One playing a minor role exceptionally (5)
I believe the answer is:
extra
I believe this clue is a double definition.
'one playing a minor role' is the first definition.
'exceptionally' is the second definition.
(thesaurus)
(Other definitions for extra that I've seen before include "Bit part actor" , "he plays his part" , "Actor's part" , "score (not a hit)" , "No great contribution to film" .)